How much of a threat is smallpox?

Characterized by fever and a distinctive type of rash, smallpox was
once one of the leading health threats facing the human species. Caused
by a virus, smallpox used to kill up to a third of the people who developed
the illness.

However, by 1980, smallpox was effectively eliminated as a public health concern,
thanks to a major campaign conducted by the World Health Organization. The last
known case - anywhere in the world - was reported in the late 1970s. Since no
animals other than humans are known to carry or transmit smallpox, the risk of
getting the illness had effectively been reduced to zero.

Unfortunately, smallpox may not be completely behind us. A few samples
of the smallpox virus were kept for laboratory use after the illness was
eradicated - and there is now reason to believe that the virus may have
been adapted for use as a weapon. The possibility of a smallpox outbreak,
caused by a deliberate release of the virus, is now regarded as a real
possibility. The likelihood of a terrorist attack using smallpox is thought
to be very low. However, the consequences of such an attack - if it did
occur - would be very serious.

What are the symptoms of smallpox?

The symptoms of smallpox begin with a high fever, head and body aches
and, in some cases, vomiting. After two to four days, a rash appears.
The rash spreads, and develops into raised bumps that crust and scab over.
After about three weeks, the scabs fall off, leaving pitted scars.

How long does it take to develop smallpox, once you're exposed? And
when do you become capable of infecting other people?

The first symptoms of smallpox usually show up about 12-14 days after
a person has been exposed to the illness, although symptoms can take
as little as seven days or as long as 17 days to appear. Once the first
symptoms appear, the patient is usually too ill to travel or engage in
most forms of activity. The patient doesn't become infectious - capable
to transmitting the disease to others - until the rash appears.

How contagious is smallpox?

Smallpox is contagious, but it's spread less easily than illnesses like
influenza or measles. Generally, it takes prolonged, face-to-face contact
- of the kind that takes place in a household setting - to spread the
disease from one person to another. It can also be spread through direct
contact with body fluids, or objects like bedding and clothing. It can
also be spread through the air in buildings or other enclosed spaces,
although that happens less commonly.

Is there a treatment for smallpox?

There is currently no proven treatment for smallpox. However, it can
be prevented through vaccination.

The vaccine can still protect people even after they've already been exposed
to the smallpox virus. While no vaccine offers perfect protection, vaccinating
within three days after being exposed to smallpox offers the same level
of protection as getting vaccinated before you’re exposed.
Vaccinating within seven days will tend to lessen the severity of any
illness resulting from exposure to smallpox.

However, the vaccine can cause serious, potentially fatal reactions
in some people, so the benefits of vaccination need to be balanced against
the risks. At a minimum, it's been estimated that roughly one out of
every million people who receive the vaccine will die - and 15 will become
very seriously ill. And unless someone does use the disease as a weapon,
the risk of becoming ill with smallpox is zero.